Electrical coils



22, 1958 F. J. T. BATEMAN 2,832,055

' ELECTRICAL com;

Filed Dec. 3, 1954 EXCESS STMP d n EXCESS EXCESS STRIP M exa-:55 srmp slm? /m/vroR 4,United States Patent ELECTRICAL COILS Fredrick .lohn Thomas Bateman, Rugby, England, as-

siguor to The British Thompson-Houston Company p Limited, a British company s Application December 3, 1954, Serial No. 472,975

Claims priority, application Great Britain December 7, 1953` 5 Claims. y(Cl. 336--192) parallel to the axis about which the coil is wound (here` inafter referred to as the coil axis) and with successive turns of the wound strip at progressively increasing mean distances from the coil axis, the axial length of the coil thusapproximating to the widthof the ystrip while the dimension of the coil between its'inner and outer peripheries is biilt up by the successive turns of the strip.

Rectangular coils wound in the above manner tend to distort when carrying heavy currents, and kmoreover the The invention, together with further objects and ad`- vantages thereof, will be more fully'understood from the following description taken in conjunction with the accompanying drawing in which:

Figs. l and2 are respectively front and side elevations of a known form of current transformer coil,

Figs. 3 and 4 are corresponding views of a current transformer coil embodying the invention, and

Figs. 5 and 6 illustrate an advantage of a triangular coil wound with the thickness of the constituent strip parallel to the coil axis, as compared with a rectangular coil similarly wound. j

Referring to Figs. l and 2, the known form of coil 1 has the generally rectangular configuration seen in Fig. 1 and is constituted by a continuous strip 2 of copper or other conductive material wound with the width of the strip parallel to the coil axis 3. Suitable insulation is of course provided `between `the adjacent turns of the coil in any convenient manner. Connecting leads 4 and 5 extending parallel to the end planes 6 and 7 of the coil 1 from the middle of the coil side 1 are connected respectively to the ends of the coil strip 2 by means of lapconfiguration of the coils and the position ofthe ends of n the constituent strip are a source of some diculty or at least inconvenience when it comes to securing connecting leads to the coils and insulating the coils and leads as by taping. For instance the connecting leads are commonly in the form of initially separate substantially rigid members arranged to extend outwardly from the coil substantially in the respective end planes thereof; it is often alsov desirable that the connecting leads shall kbe lapjointed to the coilstrip, and since the ends of the wound strip lie respectively on the inner and outer kperipheral surfaces of the coil such connectionof the leads tothe strip entailsthe inconvenience of bending `the leads out of their general planes so as to overlap the wound strip at said inner and outer peripheries respectively. More` over, to provide a generally symmetrical arrangement the connecting leads are usually arranged to extend substantially perpendicularly to a side of the coil from a position midway along the length of that side, and the resulting right-angular. configuration between the coil and the connecting leads tends to cause difculty in insulating the coil and leads in that it does not lend itself readily to a progressive taping technique.

It is an object of the present invention to provide an improved coil formation by which one or more ofthe above disadvantages of thefhitherto known coilscan' be alleviated. f

To this end the present invention provides in one aspect thereof an electric current transformer coil of generally triangular, preferably equilateral, configuration wound from electrically conductive strip and having connecting leads therefor extending from a corner of the triangle in a direction away from the coil axis so as to make an obtuse angle with each of the two coil sides adjacent that corner, the strip preferably being wound with its thickness substantially parallel to the coil axis and with successive turns offset with respect to each other axially of the coil, so that the axial length of the coil is built up by the successive turns while the dimension of the coil between its inner and outer peripheries approximates to the width of the wound strip.

joints 8 and 9, and it will be noted that since the ends of the strip 2 are respectively on the outer and inner peripheries of the coil 1, the upper ends of the connecting leads 4 and 5 have to be bent at right-angles to permit these joints to be made. y The coil 1 is bound by insulating tape 10 and it will be appreciated that the `right-angle defined between the leads 4 and 5 on the one hand and the coil side 1 on the other tends to cause some difiiculty or at least inconvenience when taping the coil and leads in that region.

Turning now to Figs. 3 and 4, the coil 11 in accordance with the invention has a triangllar form (as seen in Fig. 3) and is constituted by copper or other conductive strip 12 which, in accordance with an important feature of the `invention which avoids having to bendy the connecting leads 14 .and 15 in order tolap-joint them with the opposite ends ofthe strip 12, is wound with the thickness of the stripv parallel to the coil axis 13 and successive turns axially offset with respect to each other. This forms the edgewise wound strip into a maximum strength coil configuration with the coil strip wider dimension substantially perpendicular to the axis of the coil.- Suitableinsulation is provided between'the adjacent turns of the coil, for exampleby inserting separate insulating strips between theturns or, as has ybeen assumed in the drawing, by using conductive strip 12 which is initially covered with insulating material in any suitable manner. The connecting leads 14 and 15 extend outwardly from one corner of the coil 11 and it will be observed that since the opposite ends of the strip-12 nowlie substantially inthe end planes 16, k17 of the coil, the leads 14 and 15 can extend parallel to these planes and'be lap-jointed tothe stripr 12 without requiring their upperendsto be bent at right angl-es as with the known form of coil illustratedv in Figs. l and 2.

An .advantage of the triangular configuration of `the coil 11 in accordance with the invention is that by virtue of the obtuse angle formed between the leads 14 and 15 on theone hand and the adjacent coil sides 11 on the other hand (see Fig. 3) insulation of the coil by insulatingy tape 20 applied by a progressive taping technique is great` ly facilitated and this advantage may be further enhanced by Lsecuring between lthe leads 14 and 15 an insulating block 21 so formed as to provide a smooth curvilinear ktransition (again see Fig. 3) between the leads 14 and 15 and the coil sides 11.

Instead of insulating the coil 11 by binding it with insulating tape 20 it may be insulated, in accordance with a practice that is becoming more common, by encasing it in a thermo-setting insulating material. With rectangular coils such as that Vshown in Figs. 1 and 2 trouble is sometimes experienced with such insulation due to distortion of the coil when carrying current, and it is contemplated that the triangular configuration of the coil of the present invention may also be advantageous 'in helping to alleviate this diiculty, if as is anticipated, the deection of the sides `of a triangular coil when carrying current is less than for a rectangular coil, thus giving rise to less likelihood of such deflection causing cracking of a thermosetting insulation encasing the coil. Where the coil 11 is insulated by encasing it in a thermo-setting insulating material instead of by taping it, the oblique angle between the connecting leads 14 and 15 `and the adjacent coil sides 11', with smooth transition from one to the other provided by a block such as 21, is still preferable to the right-angle between the leads 4 and 5 and the coil side 1 in the known coil form of Figs. l and 2 in view of the smoother overall configuration obtained for the complete coil assembly.

With the coil wound with the thickness of the constitucnt strip parallel to the coil axis as in Figs. 3 and 4, further advantages may accrue from the triangular coil configuration as compared with the hitherto usually rectangular configuration. For instance it may be desirable when forming coils of strip wound in this manner to wind a large number of turns from a length of strip and to cut from `the resulting large coil a number of smaller coils identical with each other and having the required number of turns. In the case of oblong or rectangular coils this would entail cutting the wound strip either always at the middle of the same side of the coil or at the middles `of `opposite sides alternately. However the requirement that the strip forming each individual coil shall over-lap substantially the whole width of the connecting leads secured thereto, taken in conjunction with the desirability of such leads being centrally disposed with respect to a side of the oblong or rectangular coil for the sake of symmetry, precludes the strip from being terminated at the middle of that side; accordingly it would be convenient to obtain such small rectangular coils from a large one by alternately cutting mid-way along the sides of the coil adjacent the side to which the leads are to be connected. This is illustrated in Fig. 5 for a rectangular coil cut from a larger one wound from strip having its thickness parallel to the coil axis. The ends of the strip for the small coil are at 22 and 23 Irespectively, and it will be noted that each small coil would thus involve wasting a length of strip equivalent to the len-gth of the coil side at which the leads are attached less the width of the leads h plus half the length of each of the adjacent sides. On the other hand with a triangular coil configurati-on the cutting of a large coil into smaller ones to which leads are to be attached at a corner can be effected at the middle of the sides adjacent that corner as illustrated at 24 and 25 in Fig. 6, so that the wasted strip involved is equivalent to the sum of half the lengths of each of the sides adjacent the corner less the width of the leads. The wasted strip is thus considerably less with a triangular coil than with a rectangular one, it being appreciated that normally the excess strip would be removed subsequently to the cutting operation.

A further advantage of a triangular coil wound with the thickness of the strip parallel to the coil axis in the manner indicated is that with equal sides for the triangle, equal lengths of strip will require to be fed (generally au tomatically) to the bending mechanism of the winding machine for all sides of the coil, whereas for an oblong or rectangular coil dilerent lengths of strip would have to be fed alternately to the bending mechanism, making automatic operation more difficult. Moreover the winding strip requires to be bent only three times for each turn of the coil as against four times in the case of a rectangular coil, thus enabling speedier winding of the coil.

What I claim is:

l. An electric current transformer coil comprising at least one convolution of electrically conductive edgewise wound strip, which coil is of generally triangular configuration with the wider dimension of said strip substantially perpendicular to the coil axis, and connecting leads therefor extending from a corner of the triangular coil in a direction away from the coil axis so as to make an obtuse angle with each of the two coil sides adjacent to that corner.

2. An electric current transformer coil as claimed in claim 1 having positioned outwardly thereof at the corner of the triangle from which the leads extend a suitably shaped insulating member providing an effectively curvilinear transition between the leads and the adjacent coil sides.

3. An electrical current tranformer coil comprising a plurality of convolutions of electrically conductive edgewise strip wound, and successively convolutions otset with respect to each other axially of the coil, which 'coil is of generally triangular configuration with the thickness of said strip substantially parallel to the coil axis and'connecting leads therefor extending :from a corner of the triangular coil in a direction away from the coil axis so as to make an obtuse angle with each of the two coil 'sidesadjacent to that corner.

4. An 'electric current transformer coil as claimed in claim 3 having positioned outwardly thereof at the corner of the triangle from which the leads extend a suitably shaped insulating member providing an effectively curvilinear transition between the leads and the adjacent coil sides.

`5. An electric current transformer coil as claimed in claim 3 in which the conductive strip terminates at positions respectively midway along the two coil sides adjacent tothat corner of the triangle from which the connecting leads extend.

References Cited in the le of this patent UNITED STATES PATENTS 1,539,928 Angus IuneZ, 1925 2,251,776 `Ballard Aug. 5, 1-*941 FOREIGN PATENTS 4191,550 Great Britain Jan. 18, 1.923 625,908 Germany Feb. 17, 19,36 677,918 Great Britain Aug. 27, 1952 

